The present invention relates to an improved method for locating and mapping anomalous terrestrial heat flows such as occur from geothermal resources oxidizing ore bodies, unknown subterranean heat sources or heat sinks, man's environmental surroundings, and atmospheric hydrological heat sources and sinks that transfer a small, telltale temperature anomaly to the surface terrain, by characterizing the spectral, spatial, statistical, thermal, and temporal features of radiation emitted by natural terrestrial surfaces with sufficient accuracy to remove ambient, normal-surface effects.
Geothermal resources offer a promising, economically competitive, new energy source which would be developed more readily as a result of this invention. The U.S. goal is to stimulate commercial production of 20 GW of geothermal power by 1985. This would save the equivalent of 10 billion barrels of oil. The potentially valuable geothermal resource base occupies a vast 390,000 km.sup.2 of land throughout the western third of the conterminous U.S. However, little is known of the exact location, size, or potential of promising resource areas characterized by anomalous heat flows from 50 to 50 times average. Detailed surface thermal surveys needed to assess these areas are impractical until we develop more effective and less costly exploration methods.
To interest utilities in developing a new geothermal field, at least two years and $3 to $6 million must be spent proving that the field has a potential of 200 to 400 MW. Near-surface heat flow measurements, requiring about 60 man-years per 100 km.sup.2, necessitate a speculative investment of some 1 or 2 y and $2 or $3 million prior to deep exploratory drilling of areas without proven potential. Commercial enterprises are reluctant to make these speculative investments. An effective aerial temperature-sensing survey method for locating and mapping geothermal resources with near-surface heat flows from 5 to 50 times normal would reduce to a small fraction the cost (in both time and money) of existing methods. This would make practical large-scale evaluations of geothermal resources and stimulate commercial power developments.
Orthodox applications of aerial temperature-sensing surveys have been ineffective for locating or mapping geothermal heat-flow anomalies less than 50 to 500 times the global average (1.5 .mu.cal cm.sup..sup.-2 s.sup..sup.-1). The problem is: the true surface temperature for most natural surfaces cannot be derived from the measurements; available instrumentation is not specifically designed to minimize radiometric noise for accurately measuring surface temperature enhancements as small as 0.05 to 0.5 K over areas larger than 0.1 km.sup.2 or for detecting from two to five simultaneously measured atmospheric infrared bands where radiation emitted by natural surfaces (e.g, vegetated areas, sands, clay minerals, soils, rocks, and water) behaves as a featureless (graybody) spectral source; furthermore, standard procedures for interpreting the data from infrared surveys offer no way of correcting for the effects of surface emissivity variations (equivalent to temperature uncertainties of 0.5 to 5 K) assoiciated with natural terrestrial surfaces, or the intervening atmospheric path, or for reflected sky radiation; in addition, the measurement procedures are not usually optimized to reduce the effects of normal temperature variations associated with atmospheric conditions, hydrological and topographical variations, and surface compositional differences; and further, it has been assumed by many an unattainable goal to distinguish both real and apparent thermal anomalies associated with non-geothermal effects from true surface temperature enhancements resulting from subterranean sources of heat.